Process for recovering viscous crude oil from unconsolidated formations



Unite This invention relates to a process for the recovery of mineraloil from subterranean formations. More particularly, the presentinvention is concerned with a process for the recovery of oil by thermalrecovery means involving the use of a hot, upwardly how of inert gas insubterranean oil-bearing formations characterized by unconsolidatedsands or friable structures such as is indigenous to the regionsurrounding the Athabasca river in northern Alberta, Canada, and thewestern region of the United States. These unconsolidated or friablestructures are porous and are either of a fluent nature, i.e. theycrumble under the weight of the overburden or they are held together byhydrocarbons such that if the hydrocarbons are extracted as withtoluene, the sands collapse. The sands are readily distinguishable fromoil shale which is consolidated and non-porous.

In the region surrounding the Athabasca river in Alberta, Canada, largedeposits of tar sands exist. The significance of these deposits as apotential source of oil is apparent since they contain, it has beenestimated, about 200 billion barrels of oil. The oil present in Althabasca tar sand frequently has a gravity of between about 5 and 15 API andis present to an extent of about to 20 weight percent. The recoveryproblem, however, presents a number of difliculties, both from atechnical and an economic standpoint. Proposals have been made to minethe sands and recover oil from the mined sand by various operationsrequiring mechanical preparation followed by washing or heating methods.The cost of these operations, were they to be performed on a largescale, would be excessive both in terms of capital investment andoperating expenses. In the western region of the United States therealso exist unconsolidated subterranean sands bearing heavy mineral oilswhose recovery presents problems similar to those faced in the Athabascaregion except for climate and transportation considerations.

Various methods have been devised for the recovery of oil and gas fromsubterranean formations, which, at this time, may be termedconventional. These methods are to 'a great extent, supplementary toeach other and can be presented in the order in which they are appliedto a given formation. In the first instance, upon the establishment ofcommunication from the surface of the earth to a subterranean oil andgas bearing formation, the oil and gas are frequently forced through thecommunication means to the surface under the pressure prevailing in theformation. Following the exhaustion of a significant amount of pressurein the formation such that the natural flow of oil up the well bore"ceases, recovery of the oil is continued by pumping means. However,when a negligible amount of oil flows freely to the Well for pumping,the formation is sometimes repressured to drive the oil from theformation to the well. When repr'essu'ring is inexpedient, the oil canbe forced into the well from an adjacent formation by driving a liquid,e.g. water, or gaseous medium through the formation as from an input toan output well. The processes employed to recover oil, after pumpingbecomes disadvantageous, are sometimes referred to as secondary recoverymethods.

In more recent times, thermal recovery methods have become of interestfor application to the oil-bearing foratent mations to enhance oilrecovery. Such thermal means have often been proposed to effect moreefficient oil recovery whereby the thermal energy is introduced into theformation by means of hot liquids or gases.

The present invention is advantageous since conventional methods for therecovery of oil from subterranean formations are inadequate when dealingwith oil-bearing strata comprising unconsolidated sands or friablestructures of the character found in the Athabasca and western UnitedStates region, which contain heavy oil of less than about 20 APIgravity, e.g. about 5 to 15. The invention relates to a process whichemploys thermal means to recover oil from such formations havinguninterrupted vertical permeability, that is, the formation isessentially devoid of impermeable structures such as shale, clay and thelike positioned to block upward flow of gas. This vertical permeabilityextends through the oil bearing sand for at least about 50 feet andpreferably at least about feet for economical operation. In using theterm vertical I refer to a generally upward direction.

In my process, hot inert gas is introduced into a lower portion of theunconsolidated formation and conducted upwardly through the formation,eg for at least about 50 or 100 feet. The gas is then withdrawn from theformation by any suitable means providing an area of reduced pressure toinsure the upward direction of gas flow. Thus, the oil-bearing formationis progressively heated from a lower to an upper region and as this isaccomplished the heavy oil flows downwardly through the formation,countercurrent to the flow of gas, to a point or collection area whereit can be recovered by suitable means, for example, by pumping or by agas lift. Conveniently, the oil collection point is at or below theposit-ion of upfiowing gas introduction. After the formation has beenheated to about 500 [to about 800 F., preferably about 600 to about 750F., for a vertical distance of at least about 50 or 100 feet, the upwardflow of inert gas may be discontinued, and a downward flow of inert gasapplied to the formation to drive the oil to the recovery point orcollection area. The introduction point of the gas in the latteroperation is usually spaced vertically at least about 50 feet,preferably at least about 100' feet, above the point of introduction ofthe upflowing gas. Conveniently, the downfiowing gas is introduced intothe formation at the position of withdrawal of the upflowing gas, andthe downflowing gas is withdrawn from the formation where the upflowinggas is introduced.

The gases used in my process are inert to combustion and will include COfuel gas, CH N etc. and no or only small amounts of O insufficient tocause any significant combustion of hydrocarbons present. The gas maycontain free hydrogen which could serve to increase the hydrogen tocarbon ratio in the oil and decrease its viscosity. Although I prefersubstantially no free 0 in these gases, the permissible amount of 0which can be tolerated is variable and depends primarily upon thetemperature and the character of the introduced gas and the hydrocarbonsand carbon deposits in the formation. The temperature of the gaslikewise depends upon the char acter of the formation and thetemperature desired therein; however, temperatures for the upflowing gasin the range of about 500 F. to about 800 F. are usable althoughtemperatures in the range of about 600 F. to 750 F. are preferred andabout 700 F seems optimum. The downflowing gas can be introduced intothe formation at any temperature of up to about 800 F. Preferably, thisgas is at ambient temperature or at the temperature at which it isavailable to the working site. The downflowing gas is inert as describedabove and the gas might be produced in-situ through heating of aninjected liquid such as Water or light hydrocarbons.

The superficial velocity of the gas passing upwardly through theformation is also dependent upon the nature of the formation. Since theresidual oil in the formation flows counter to the gas flow, thevelocity of the gas is limited to a maximum which will not adverselyaffect the flow of oil, e.g. a maximum of about 60 feet per minute. Theminimum velocity is determined by heat requirements in the heating ofthe formation as well as economical considerations, and is usually atleast about 0.1 foot per hour; however, a superficial velocity in therange of about 1 foot to about feet per minute is preferred. Thevelocity of the downflowing gas can be as desired but, of course, thepressure of introduction must be sufiicient to maintain gas flow. Theupward and downward flows of gas are conducted through a section of theformation extending, from the point the gas is introduced into theformation, vertically to about 30 from the horizontal to the point ofintroduction, preferably from vertically to about 60 from thehorizontal. The gas used in my method can be heated either on thesurface or by a heating unit or burner in the well.

The advantage in using any upflowirrg, heated gas was shown in a smallscale experiment. Thus, a sand pack, representative of the Athabasca tarsands, having.

an initial permeability when cold of 110 ft. /hr. of gas at 27.5 psi.was subjected to downflowing hot inert gases, and the flow of gas ceasedat 90 p.s.i. in less than one hour. It is believed that the cause ofblockage was due to the flow of hot oil, of a viscous character, intocold sand where it became solid or immobile, thus plugging all availablegas pore space.

The feasibility of my method has been confirmed in a test using a 1072gram quantity of simulated Athabasca tar sand containing 14.9 percent byweight of 10 API gravity, 500 SUS viscosity at 210 F. residual SouthTexas crude bottoms and 85.1 percent by weight of builders sand, a 100gram sample of which was analyzed using a screen test, with thefollowing results:

Retained on screen: Quantity, grams A 2 steel tube (3.35 square inchesin cross-section) in length, packed with 1072 grams of theabovedescribed simulated Athabasca tar sand, and having a A" nippledopening at each of its two ends, with the lower nipple containing abubble cap to prevent sand clogging while gas is passed freelytherethrough and into the sand pack, is vertically and centrallydisposed in a cylindrical container. extends downwardly with the nippleprotruding through a close-fitting opening in the bottom of the tank.Another line used, for the recovery of oil accumulating in the bottom ofthe tube, provides communication means downwardly from the bottom of thetube, through the bottom of the tank and into an oil receivingcontainer. Three sets of electrical heating coils are placed around thetubing and are vertically spaced up the tubing. The container holdingthe tube contains insulation to minimize heat losses. The depth of thesand pack in the tube is 12".

The process of my invention is confirmed using the above material andequipment in the following manner. During a 3-hour period, 24.22 cubicfeet of cool engine exhaust gas, at an average rate of flow of 0.16cubic foot/min, and an average superficial velocity of 6.85 feet/min.are conducted upwardly, through the capped nipple of the tube, thepacked sand, and is vented through the top nipple. The heating coilsserve to heat the gas The end with the capped nipple and sand pack andthe average temperature of the bottom section of the sand is 437 F. Themiddle section of the sand has an average temperature of 500 F., whilethe top section has an average temperature of 450 F. Seventeen grams ofoil, essentially of the same gravity as that initially mixed with thesaid are recovered. After the 3-hour period, using the same sand pack,and during a 65-hour period; 12.58 cubic feet of engine exhaust gas, atan average rate of flow of 0.032 cubic foot/min. and an averagesuperficial velocity of 1.37 feet/min. are conducted, in the same manneras the previous volume of gas, upwardly through the capped nipple, thepacked sand, and is vented at the top nipple. The average temperaturesof the sand are: bottom section, 603 F.; middle section, 663' F.; andtop section, 703 F. Fortyone grams of oil, essentially of the samegravity as the initial charge, are recovered through the oil recoveryline.

Following the above sweep of gas upwardly through the tube, the gas flowis reversed and the sand pack is swept with a downward flow of gasduring a 8.16-hour period. 49.46 cubic feet/min. of engine exhaust gas,at an average rate of flow of 0.1 cubic foot/min, and an averagesuperficial velocity of 4.30 feet/min. are conducted downwardly throughthe top nipple of the tube, the sand pack, and passed, along with theoil, through the oil recovery line. The average temperatures of the sandpack are: top section, 703 F.; middle section, 663 F.; and bottomsection, 603 F. Eighteen additional grams of oil, essentially of thesame gravity as that initially mixed, are recovered through the oilrecovery line. Thus, 47 .5- weight percent of the initially mixed oil isrecovered by this procedure.

Field use of my method as applied to Athabasca or similar sands willmost advantageously be employed on formations of the greatest thicknessat the least available depth. Well patterns or other access to theformation can be developed along several lines. For instance, verticalwells can be drilled to the position of introduction of the upflowinggas, and the gas may exit in the upper portion of the same well or in aspaced or adjacent output Well. Then the downfiowiug gas, if used, canbe applied in the reverse path, and oil is recovered from the welllocation of initial gas input. Access out into the formation fromvertical Wells can be effected by horizontal drilling at the desiredpoint. Also, horizontal access can be made from a natural outcrop of thesand.

In a typical example of my process, a well is drilled from the earthssurface to the bottom of a formation of Athabasca tar sand 200 feet inthickness, and then horizontally away from the vertical bore for fiftyfeet. The well is cased and a liner is inserted in the horizontal hole.A second well, located 50 feet from the first and near the ends of thehorizontal hole of the first Well, is drilled from the earths surface tothe top of the tar sand formation and then horizontally for 50 feettowards the first well. The second well is cased and lined similar tothe first well. An internal combustion heating unit is inserted into thefirst well and it heats flue gas passing downwardly into the well to atemperature of 700 F. The heated flue gas, at a superficial spacevelocity of 9 feet/min, is conducted through the liner, and upwardlythrough the formation, which is progressively heated thereby, to thesecond well or the gas takeoff well where the gas is recovered andrecycled. Residual oil in the formation, flows downwardly to the bottomof the first well where it is pumped out and recovered. After theformation is heated to a temperature of 700 F., the flow of gas at thesame velocity is reversed, i.e. into the second well, downwardly to thebottom of and out of the first well; thus sweeping additional amounts ofoil to the bottom of the first well from which it is recovered. No

a heater is used in the second well during reverse gas flow.

I claim: 1. A method for the recovery of heavy oil from a 5 formation ofunconsolidated sands having vertical permeability, said oil having anAPI gravity of less than about 20, the steps comprising introducing hotinert gas at a temperature from about 500 to 800 F, into a lower portionof the unconsolidated formation via a well therein, conducting the gasupwardly through the formation at a superficial velocity of about 1 footto 10 feet per minute to progressively heat the formation from a lowerto an upper region at a rate sufiicient to allow the heavy oil to flowdownwardly through the formation to an area of collection adjacent thelower portion of the formation, and continuing to conduct the hot inertgas upwardly through the formation to maintain the progressive heatingby contacting the formation from a lower to an upper region by takingoil gas in the upper portion of the formation 15 2,857,002

References Cited in the file of this patent UNITED STATES PATENTS1,816,260 Lee July 28, 1931 2,421,528 Stelfen 'June 3, 1947 2,813,583Marx et al Nov. 19, 1957 2,819,761 Popham et a1. Jan. 14, 1958 Pevere etal Oct. 21, 1958

